Spark plug



May 29, 1934- H. J. MUIR 1,960,344

SPARK PLUG Filed sept. 8, leso Illl Patented May 29, 1934 193609344 Harold J. Muir, Chicago, Ill., assigner to Animated Spark Plug Company, Chicago, Ill., a corporation of Illinois Application September 8, 1930, Serial No. 480,378

3 Claims. (Cl. 12S- 169) This invention relates to improvements in spark Figure 2 is a transverse sectional view of the plugs, particularly of the type for employment in same taken on the line 2-2 of Figure l, looking internal combustion engines and While the invenin the direction indicated by the arrows. tion is described and illustrated as incorporated Referring now more particularly to the draw- 5 in a type oi spark plug having one insulated tering, wherein a preferred embodiment of this in- 6o minal and a grounded sparking terminal complevention is illustrated, provide a metallic casing mental thereto, it will be understood that the inor shell 5. This casing or shell is provided with vention may be applied to other types of spark a bore 6 formed with a shoulder 7 and the outer plugs and that it it, therefore, finds a wide eld internally threaded portion 8. The outer end 10 of utility. thus internally threaded is externally polygonally 65 The principal objects and advantages of this formed as indicated at 9 to permit of the applicainvention reside in the provision of an improved tion of a wrench for inserting the spark plug into type of spark plug wherein improved means for a combustion chamber on into the cylinder head admitting cleansing and cooling air to the vicinity oi an internal combustion engine. The casing 5 of the sparking terminals of the electrodes is prois provided with a cylindrical portion l0 which is 70 vided; the provision of an improved form of spark externally threaded as at 11 to facilitate engageplug in which fresh air or atmospheric air is adment of the spark plug in a suitably threaded mitted to the vicinity of the sparking terminals opening in the internal combustion engine, usufor increasing the degree of combustion and ally provided in the cylinder head thereof.

thereby preventing accumulation of carbon and The cylindrical wall or" portion 10 also serves 75 other fouling matter thereon; the provision of an to Support the sci-called grounded electrode 12 implOVed Spark plus and means fOI' admitting which is ixed in a suitable aperture longitudinalatmospheric air at the vicinity thereof in an enly of the wall l0 and projects toward the axis of gine cylinder, in combination with means for prethe cylindrical bore 6 as is the conventional conventing backfiring through the spark plugs; the structionof spari; plugs, '85

DlOVSOIl Of en IIlDTOVed Spark Dhlg Of the type A central or axial insulated electrode 13 is proreferred to wherein fresh air or atmospheric air vided and mounted in an insulating support 14 is permitted t0 enter adjacent to the sparking telwhich may be constructed of any suitable heat minals but is excluded from direct COIltaCt UDCH resisting insulating material such as pressed as- .30 entry with the insulating element or elements so bestos, porcelain, 0r the like, The insu- 85 aS t0 prevent undue heating and thereby dSIlte lating support le is substantially cylindrical gration of the insulating element. throughout substantially half of the length there- This invention has, as a further object, the proof and is annularly enlarged as at 15 to seat upon vision of an improved means of the character rea suitable metallic packing ring 16 mounted on ferred to which is capable of application either to the shoulder 7. 90 spark plugs having a single insulated terminal or A retaining gland nut 17 is in engagement with to spark plugs in which both terminals are inthe internal threaded portion 8 by the provision sulated from the casing or shell of the plug, and of a cylindrical extension i8, the nut having'an wherein the application of this invention may be annular internal :Flange 19 engaging the outer end 40 had Without Changing the Deltula Spark plug of the enlargement 15 and thus impinging said 95 in size as to outside dimension so that the article enlargement on, the packing 16 and iixedly retainwhen produced according to this invention is of a ing the insulating supporting member against substantially standard size and external contour rotative and longitudinal displacement and at the thereby ObVtIlg the leCeSSty fOr Special tools same time forming a fluid-tight joint; that is,

45 or special fittings to permit of its commercial a joint which will prevent the escape of gases 100 adaptation to existing internal combustion enfrom, the combustion chamber. gines and the like. I nud that in a spark plug made according to The foregoing and such other objects and admy invention, a greater intensity of heat is present vantases as may appear 0r be pointed Out as this immediately adjacent to the electrodes due to the deSCIDtOIl DTOCeedS are attained ih the Stl'llC- admission oi oxygen in the air passing to the 105 tural embodiment of the invention illustrated in vicinity of the sparking terminals and, therefore, the accompanying drawing in which: iind it desirable to mount the insulated electrode Figure l is a longitudinal sectional view 13 in the supporting member ill so that the unthrougha spark plug including the improvements equal expansion and contraction of these eleof this invention; and ments will not cause fracture of the insulating 11o support. To this end, the electrode 13 extends upwardly through the support 14 into an enlarged extension member 20 which projects beyond the upper end of the insulating support to form an insulating post 21 on which a retaining nut 22 is threaded. The outer end of the electrode 13 is received in a bore 23 provided in the threaded extension 20 and is fixed therein by soldering or any other desirable means, the electrode and said extension 20 being retained and sealed in position in the support 14 by the introduction of a heat resistant and insulating cement 24. This physical contact or connection between the electrode 13 and the insulating support 14 is limited to a point adjacent to the outer end of the electrode 13 thus affording a space 25 between the electrode and the insulating supporting member 14 thereby permitting the expansion and contraction of the electrode without fracture of the insulating support or chipping of the same at its narrowed tapered end indicated at 26. The space 25 afforded is of limited degree so that for all useful purposes the electrode is well supported substantially throughout its entire length.

In order to facilitate combustion, keep the electrodes and the insulating member relatively cool and to prevent pitting of the electrodes and the collection of carbon and other deposits on the spark plug terminals, I provide at least one air duct or passageway in the cylindrical wall 10, it being understood that any reasonable number of these ducts may be provided without departing from the spirit of the invention. The drawing shows two such ducts, 27 and 28, and two controlling means therefor. As the ducts 27 and 28 and their respective controlling means are identical, I will describe but one of the same.

The duct 27 has an outlet 29 to the combustion chamber adjacent to the sparking terminals 12 and 13 and admits air to this vicinity, but excludes air upon entry from direct contact with the tapered portion 26 of the insulating support. The duct 29 extends up through the cylindrical wall 10 and terminates in an enlarged external annular iiange 30 which is intended to abut the outer wall of the cylinder head when the plug is inserted into position. The duct or passageway 27 thus communicates wth an inner recess 31 extending radially of the spark plug casing or shell and located within said annular flange.

The recess 31 is adapted to receive and contain a check valve element 32 having a seat 33 and a stem 34 projecting through an aperture 35 in a valve cage 36, which latter is provided with a suitable valve seat and extends into the recess 31 to retain the check valve in position and to form a seat member therefor.

It will be observed that the inner cylindrical portion 37 of the cage 36 is left plain both as to its periphery and as to its end edge 38 so that it forms a firm seat in the inner end of the recess 31.

It will be understood that upon each reciprocating motion of the piston in the internal combustion engine, which has been omitted from this drawing, the check valves will be opened and closed to afford entry of fresh air at atmospheric temperature to the vicinity of the sparking terminals. Owing to the intense heat thus generated, I have found it desirable that the air thus admitted be deflected away from the insulating supporting member' rather than directly upon it as this not only will crack the insulating member but actually will reduce it in some cases to a molten state, particularly where the spark plug is employed in the so-called high-pressure type of automobile engine where high-test fuel is regularly employed.

It will be understood by those skilled in the art that, due to the intensifying of the spark and the resultant heat generated, brought about by the admission of fresh air, at the Vicinity of the spark, and the proximity of the narower or tapered portion of the insulator to this locality, and coupled with the increase above normal of the distortion of the electrode (expansion and contraction), fracture of the insulator at this point is imminent, but applicant by spacing the electrode for most of its length from the wall of the opening in the insulator, or conversely supporting it from a relatively small area, air is permitted to circulate within the opening, thus cooling the insulator and the electrode and, therefore, at no time can the unequal expansion or contraction of the electrode and insulator produce unequal stresses therein and fracture or chipping from these causes is thus substantially eliminated.

I claim:

1. In a spark plug, an outer conducting shell or casing and a sparking terminal carried by the inner end thereof in operative position, an insulating member in said shell having a tapering inner end and provided with an axial opening, an electrode supported near one end in and of less iameter than that of said opening and extending beyond the inner tapered end of said insulating member so as to be free to expand and contract without contact with the major portion of said opening, means for admission into and discharge of fresh air only to the vicinity of said sparking terminal and away from the inner end of said insulating member for intensifying the spark produced thereby, the space between said electrode and the wall of said opening permitting circulation of air therein for cooling the insulating member, and the free mounting of said electrode permitting expansion and contraction of said electrode and insulator without producing destructive stresses in said insulating member, thereby preventing fracture of the insulator adjacent to said tapered end.

2. In a spark plug, an outer shell or casing and a sparking terminal carried thereby, an insulating member in said shell provided with an axial opening, an electrode supported in and of less diameter than that of said opening, said electrode extending beyond the inner end of said insulating member adjacent to said sparking terminal, means for admitting fresh air to the vicinity only of said sparking terminal and away from the inner end of said insulating member for intensifying the spark, and means near the outer end of said opening for engagement with a relatively small area of said electrode so that the same is supported in spaced relationship to the wall of the opening over a relatively large portion of its area, and thereby permitting expansion and contraction or other distortion of the electrode, due to the admission of fresh air adjacent to said sparking terminal and to thereby prevent fracture or chipping of said insulating member at its inner end, without interference by said insulating member.

3. In a spark plug, in combination, an outer conducting shell or casing externally threaded and adapted for attachment to a complementally threaded aperture in the combustion chamber of an internal combustion engine, a sparking terminal carried in operative position by the inner end of said conducting shell or casing, an insulating core member in said shell having a tapered inner end and provided with an axial opening, an electrode of less diameter than that of said opening supported within said opening only at the outer end of said opening, thus providing an annular space between said electrode and said insulating core member permitting the circulation of air therein for cooling the insulating core member, and the free mounting of said electrode permitting expansion and contraction of said electrode and said insulating core member independently of each other, thus preventing fracture of said insulator member due to destructive stresses set up by unequal expansion and contraction of different materials, said electrode also extending substantially beyond the inner end of said insulating core member to remove the point of maximum temperature from the immediate vicinity of the inner end of said core; and means, entirely contained within the walls of said shell or casing whereby fresh air is admitted through the walls of said casing at each stroke of said engine, said means comprising a longitudinal passageway in the Walls of said casing having access to atmosphere outside of the engine and a valve member at the outer end of said passageway permitting passage of air into said passageway due to suction in said combustion chamber but closing said passageway under compression in said combustion chamber, said passageway extending so that the air is admitted only at the inner end of said spark plug in the vicinity of said sparking terminal away from the end of said insulator for the purpose of intensifying the spark and causing more complete combustion in said combustion chamber. HAROLD J. MUIR. 

